The present invention is directed to a fluid dispensing device for administering liquid parenterally to a patient. More particularly, the invention relates to a fluid dispensing device useful as an ambulatory disposable drug infusion pump for accurately controlling the liquid administered parenterally to a patient.
Ambulatory drug infusion devices are known. Typically, such devices are sophisticated, computer controlled, electrically operated pumps which permit a patient to continuously receive a drug as an outpatient. The cost of these devices is great thus limiting their application.
An object of the present invention is to provide an improved ambulatory drug infusion device which is inexpensive, light-weight and disposable. A further object of the invention is to provide an improved ambulatory drug infusion device which is not operated electrically thereby avoiding the necessity of batteries, etc.
These and other objects of the invention are attained by the fluid dispensing device of the invention which comprises a reservoir for a liquid to be administered parenterally to a patient, means for placing the liquid in the reservoir under a constant pressure for dispensing the liquid from the device, and flow control means for adjustably controlling the flow rate of the liquid dispensed from the device. The flow control means according to the preferred embodiment of the invention comprises an elongated passage through which liquid from the reservoir can be flowed to an outlet of the device and means for changing the length of the elongated passage through which the liquid is flowed thereby changing the flow rate of the liquid through the passage. In the disclosed embodiments of the invention, the means for placing the liquid in the reservoir under a constant pressure for dispensing the liquid from the device comprises a spring and means for tensioning the spring once the reservoir has been filled with liquid through A means of the device for introducing liquid in the reservoir.
More particularly, according to the disclosed embodiments, at least a portion of the reservoir is formed of a flexible material to allow the reservoir to be compressed to place the liquid therein under pressure and to collapse the reservoir as the liquid is dispensed from the device. The means for placing the liquid in the reservoir under a constant pressure presses the flexible material of the reservoir to place the liquid therein under constant pressure. According to a preferred embodiment of the invention, the means for placing the liquid in the reservoir under a constant pressure comprises a compression spring and a variable helix angle translator interposed between the compression spring and the reservoir of the device, so that a constant force can be applied to the liquid in the reservoir as the compression spring extends in order to maintain the constant pressure on the liquid in the reservoir. A spring load adjuster means is provided in the device to permit adjustment of the position of the compression spring during assembly of the device to compensate for any variations in the load rate of the spring from a desired, predetermined load rate. A second embodiment of the invention comprises a constant load negator type spring and means translating a radial force of the spring into axial force for application to the liquid in the reservoir as the means for placing a constant pressure on the liquid in the reservoir.
The means defining an elongated passage in the flow control means includes a metering member having an elongated groove with a small cross-sectional area formed in a first surface thereof and a baffle member having a surface overlying the groove to form the elongated passage. The means for changing the length of the elongated passage through which liquid is flowed comprises a shunt for selectively bypassing the liquid about a portion of the elongated passage defined between the first surface of the metering member and the baffle member. According to the disclosed embodiment, the metering member and baffle member are secured against movement relative to one another in the device by bonding the two members together. At least one of the metering member and the baffle member has a plurality of spaced openings communicating with respective portions of the elongated passage defined between the members. The shunt is movable relative to the spaced openings to selectively communicate a bypass passage of the shunt with respective ones of the openings to thereby change the length of the elongated passage through which the liquid is flowed to the outlet of the device. In particular, the shunt is rotatable with respect to the assembly of the metering member and the baffle member to selectively communicate the bypass passage with respective ones of the openings in the one of the members formed with such openings. The elongated passage defined between the metering member and the baffle member extends in a serpentine shape in the illustrated embodiments. The shunt is fixed for rotation with a dial cover of the fluid dispensing device. The device further includes means permitting injection of a hypodermic needle into the device for introducing liquid into the reservoir of the device to initially fill the reservoir.
The constant force applied to the flexible reservoir in the fluid device of the invention causes a constant pressure on the liquid within the reservoir of the device. This results in a constant flow of liquid through the flow control means and outlet of the device with a given setting of the flow control means. Therefore, the device of the invention provides an inexpensive, light-weight, ambulatory disposable drug infusion pump which can be safely used in many medical applications including the administration of chemotherapy drugs for cancer patients, anticoagulant drug for patients with circulatory illnesses, pain reducing drugs for burn patients and patients with rheumatic diseases, insulin for diabetics, veterinary medicine applications, etc.
These and other objects, features and advantages of the present invention will become more apparent from the following description when taken in connection with accompanying drawings which show, for purposes of illustration only, two embodiments in accordance with the invention.